334 ALASKAN GLACIER STUDIES ,
south of Childs Glacier,1 (2) the Paleozoic Valdez group throughout the Copper River canyon to a point between Tiekel River and Spirit Mountain, and (3) a belt of meta-morphic slate, schist, and limestone, with intrusive diorite and greenstone, the limestone being in part of Carboniferous age.2 The highest peaks and the deepest, narrowest portion of Copper River canyon are at the north in this third belt of most resistant rocks, and the broadest portion is at the south in the belt of weakest and youngest rocks.
Outside of Prince William Sound the Gulf of Alaska is relatively shallow, the hundred fathom curve being forty to seventy miles offshore. Off the Copper River delta it is easy to understand why one must go about 20 miles from shore before a depth of 350 to 400 feet is reached; but off Hinchinbrook Island, where there is no such active deposition, it is also necessary to go 5 to 10 miles before a depth of 300 to 350 feet is reached. Between the mouth of Prince William Sound and Middleton Island, which is 56 miles offshore, the depth of the Pacific Ocean averages only 200 to 450 feet.
In the straits at the entrance to Prince William Sound, that is between Hinchinbrook and Montague Islands, the water is 600 to 1300 feet deep and inside Prince William Sound the water averages 600 to 2400 feet in the main sound and 400 to 1400 feet in the tributary fiords, a striking contrast with the shallower ocean outside and one that will be explained later by the conditions of glaciation. One fiord, Orca Inlet, which opens to the Pacific, is only 6 to 60 feet deep and is quite unnavigable at the mouth; making it necessary for ocean steamships bound for the town of Cordova to go over fifty miles out of the way to reach the head of Orca Inlet by way of the main Prince William Sound and Orca Bay.
There are a few small native settlements on Prince William Sound and mining settlements on Latouche and Knight Islands and an old Russian trading post, Nuchek, on Hinchinbrook Island. At the head of Port Valdez, near Shoup and Valdez Glaciers, are an army post, Port Liscum, and the town of Valdez, from which a military road extends into the interior of Alaska. Between the mouths of Valdez Arm and Port Fidalgo are EUamar and several other mining settlements. There is a salmon cannery at Orca and nearby on Orca Inlet is the town of Cordova. The Copper River and Northwestern Railway extends eastward from Cordova, crosses a mountainous peninsula through the valley of Eyak Lake, and emerges on the Copper River delta, which coalesces with the deltas of the streams from Scott, Sheridan, and smaller glaciers in the mountains. The railway crosses Copper River just east of the old native settlement of Alaganik and goes up the eastern side of Copper River to Childs Glacier, which enters from the west nearly opposite Miles Glacier, which comes from*the east. The railway crosses the river between these two glaciers and thence, after passing the Abercrombie Rapids, extends over the stagnant terminus of Allen Glacier, which enters Copper River valley from the west. Beyond this the railway follows the western side of the Copper River canyon, at the northern end of which is the town of Chitina.
Climate and Glaciation. Such precipitation records as we have in the Prince William Sound region show an annual rainfall of 190 inches at Nuchek at the western end of Hinchinbrook Island; at Orca of 149 inches; and at Port Liscum an average of 76 inches. The precipitation is heaviest in fall and winter and, therefore, much of it is snow. In this latitude, 60° 30' to 61° N., the warm waters of the Gulf of Alaska amelio-
i Brooks, A. H., Boll. 480, U. 8. Geol. Survey. 1911, PI. m and pp. 48-49. i Moffit, F. H., Bull. 520, U. 5. Geol. Surrey, 1912, PI. V and p. 94.